This invention relates in general to web tension-control apparatus and more particularly to tension-control apparatus for ink ribbons employed in serial printer applications.
Although the invention is applicable to various web, tape, strand and ribbon-like materials, it has been found particularly useful in the environment of ink ribbons as used in serial printers. Therefore, without limiting the meaning of the word "ribbon," the invention will be described in this environment.
In devices in which any web material is to be delivered or transferred from a rotatable reel, drum, spool, spindle or a like receptacle to another similar and compatible receptacle, it is normally necessary to provide means for maintaining a certain amount of tension in the web material during its deliverence. In the particular environment of ink ribbons employed in serial printers, a certain amount of tension is required for proper ribbon feed and acceptable print quality of the printed material.
As any web material is delivered between a pair of reels, drums, spools, spindles, etc., the tension therein will tend to vary due to geometrical and inertial changes. In a serial printer ribbon system, a certain amount of variation in the tension in the ribbon does not adversely affect the ribbon feed or the print quality; however, it is necessary to maintain an acceptable tension on the ribbon in order to ensure that the ribbon is taut at the printing position or station. In addition, the ribbon must be maintained under tension in order to wrap the ribbon on the take-up spool in a tight and even manner.
A fabric ribbon is less susceptible to changes in tension than the matrix type plastic ribbon since it does not stretch nor break as easily, and it more easily conforms to the physical shape of the character during the printing action. When using a matrix type plastic ribbon, an excessive amount of tension in the ribbon can cause the ribbon to stretch and wrinkle and/or fold over onto itself about the deformed center portion or to break, all of which affect the print quality. Also, an excessively low ribbon tension can allow the ribbon to move from its print position to a degree, which causes partial or total loss of printing of characters.
It is well known in the art to continuously vary the braking of the wind-off reel in dependence of the tension in the wound-off web material and to rapidly stop and wind-off reel in case of disruption of the web material as disclosed in U.S. Pat. No. 3,243,137. It is also known to use a pawl and ratchet brake device as disclosed in U.S. Pat. No. 3,442,366 to control ribbon tension in an incrementing ribbon feed system. In U.S. Pat. No. 3,621,968, a roller and spring arrangement is disclosed to provide tension in an endless ribbon within a ribbon cartridge. The present assignee is marketing an electronic typing system under the tradename of Xerox 800 Electronic Typing System, which employs a spring and dancer-arm arrangement, as shown in FIG. 1, to provide the necessary control of tension in the matrix type plastic ribbon.
Such prior art solutions have utilized moving mechanical means to provide the necessary control of the tension in the web material.
With the prior art in mind, it is an object of the present invention to maintain the tension in a ribbon-like member substantially uniform during its transfer from a supply spool to a take-up spool.
Another object of this invention is to provide a cost effective means to maintain the tension in ink ribbons contained in cartridges along the presently described vane.
Yet, another object of the present invention is to provide a simple and reliable ribbon tension control means, which is compatible with cartridges of the present type.
Other objects and advantages of this invention will be evident from the specification and claims and the accompanying drawing illustrative of the invention.